The present invention relates to a method for repairing a photomask used in manufacturing a semiconductor device comprising the step of inspecting the mask-pattern of the photomask and then repairing any defects in the mask-pattern on the basis of the inspection result.
An inspecting apparatus, used during the process for manufacturing a semiconductor devise, inspects for defects in the mask-pattern of a photomask. This apparatus has an optical system for illuminating and imaging a photomask, a sensor for acquiring the image of the photomask and outputting an image signal, and an inspection portion for inspecting the mask-pattern on the basis of the outputted image signal.
As a light source used in the optical system, a mercury lamp is generally used. The mercury lamp makes it possible to illuminate the photomask by light having wavelengths from the visible range to the ultra-violet range (around 365 nm).
Recently, the minuteness and the integrated scale of mask-patterns for a photomask have increased, as the performance of a semiconductor apparatus becomes higher. This requires an apparatus for inspecting the photomask to exhibit a higher resolution so as to detect smaller defects in the mask pattern. It is necessary to shorten the wavelength of light from the optical system to realize the higher resolving power. However, conventional mercury lamps cannot provide enough illumination intensity, in the short wave range, which can be used for the inspecting apparatus. Therefore, a laser such as an ultraviolet laser is used instead of the mercury lamp.
However, when a laser beam provides a light source for the defect inspecting apparatus, interference fringes are generated from the coherency of the laser. The generation of the interference fringes causes variations in the brightness of the acquired image outputted from the sensor; therefore, in inspecting any defect, it is impossible to decide whether this “variation” is generated from a defect in the mask-pattern or from the coherence of the laser beam.